The present invention relates to plotters generally and, more particularly, to a plotter having features enabling unattended operation thereof and to a method for automatically aligning a chart with the plotter X-axis.
Plotters convert digital information into graphic representation by using a chart and pen to produce line drawings from a series of individual points. The Cartesian coordinate system used to determine the position of these points consists of three orthogonal or mutually perpendicular axes known as X, Y, Z, the relationship of these axis to a typical plotter being shown in FIG. 2. These digital points are typically transmitted by a host computer, where they are created and stored.
In a moving-medium type plotter, both the pen and chart are moved to produce a drawing. With this type of plotter, movement in the X-axis is accomplished by moving the chart in and out of the plotter, conventionally with a single drive drum and motor assembly. Y-axis movement is accomplished by moving the pen back and forth across the chart, conventionally with a drive belt and motor assembly. Z-axis movement is simply accomplished by moving the pen up off the chart or down onto the chart, conventionally by means of a solenoid. With these basic movements, the plotter is capable of producing virtually any kind of line drawing on the chart.
In an era of ever increasing labor costs, the desirability of a truly automatic plotter--that is, a plotter having a reliable capability of unattended operation--requires no elucidation. Preferably, such an automatic plotter would be able to accommodate either cut sheet or roll chart format, accommodate chart widths of a variety of standard drafting sizes, and be inexpensive to manufacture. The creation of such an automatic chart plotter requires the confluence of a number of different innovative features. For example, the conventional X-axis drive uses a single motor to drive a large rod or drum with sprockets or friction drive surfaces to move the chart along the X-axis. Even the slight normal manufacturing tolerance differences over the length of the single rod or drum can result in a substantial unintended skewing of the plot. Thus, very long plots on roll-feed media have heretofore been possible only with the more expensive sprocketed drive mechanism and chart, and not the relatively inexpensive friction drive mechanism. Furthermore, as the single large rod or drum necessarily spans the full width of the plotter, in larger plotters the inertial load for the drive system has necessitated the use of an expensive large motor. Thus, as a first innovative feature, the truly automatic plotter requires an improved inexpensive, non-skewing X-axis friction drive mechanism. Second, an automatic plotter requires means for automatically aligning the chart with the plotter axes, especially the X-axis, during loading procedures and optionally at subsequent times. Ideally, the automatic chart alignment means used during the loading procedure cooperates with the improved X-axis motor drive so that the chart is properly positioned in alignment with the plotter axes during the loading procedure and not accidentally caused to skew therefrom subsequently by the X-axis motor drive. Third, in order to enable the automatic plotter to utilize chart stock supplied in roll form and to cut this stock to a desired length for a given plot, the automatic plotter must have a chart cutting mechanism. In order to keep the cost of the automatic plotter competitive with conventional plotters, this feature should be implemented utilizing as much as possible of the existing plotter equipment. Finally, an automatic plotter must include a cut chart handling mechanism for handling (that is, retrieving and neatly and orderly storing) cut charts of varying length, as produced by the chart cutting mechanism.
Accordingly, it is an object of the present invention to provide a plotter having an X-axis drive which avoids accidental skewing of the chart.
Another object is to provide such a plotter having an X-axis drive offering a low inertial load relative to the conventional X-axis drive.
A further object is to provide a plotter having an automatic chart alignment feature so that it can accurately align a chart with the plotter X-axis.
It is another object of the present invention to provide a plotter having a chart cutting feature which, for only a slight additional cost, enables chart stock supplied in roll form to be accurately cut to a desired length for a plot.
It is also an object to provide a plotter having a cut chart handling feature enabling the retrieval and orderly storing of cut charts.
It is a further object to provide a plotter having the capablity of unattended operation through utilization of an improved X-axis drive mechanism, an automatic chart alignment mechanism, a chart cutting mechanism and a cut chart handling mechanism.